In known Radio Frequency IDentification (RFID) systems fixed threshold levels are used for detecting data and collisions in data stream signals received by an RFID reader. In this context, the term “fixed threshold levels” means that said threshold levels are either set in advance or are selected as a predefined multiple of an input noise signal.
However, these known RFID systems have shown the disadvantage that in case of varying signal levels the threshold levels used for the detection of data and collisions cannot be adapted, which may result in detection errors. Varying signal levels may for instance arise from signal beat or from varying coupling between the antennas of an RFID reader and RFID tags, respectively.
From the document U.S. Pat. No. 5,300,922 a periodic pulse discrimination system for use with electronic article surveillances systems is known which is capable of detecting valid tag pulses while discriminating against periodic pulses caused by resonances and interfering carriers as well as random noise. Circuitry that determines the periodicity of a pulse signal and is responsive to amplitude differences between successive detected pulses controls an adaptive threshold and sampling window to discriminate against signals having an incorrect periodicity and an inadequate envelope rise time. This document generally discusses topics in respect of adaptive detection of periodic signals and noise, but does not disclose processes or means for detecting data and collisions in data stream signals among the signals of multiple RFID tags by use of adaptive threshold levels.